Peristaltic pump with a removable and deformable carrier

ABSTRACT

A peristaltic pump includes a removable carrier against which a flexible tube is pressed by rollers. The carrier includes an intermediate deformable section having an internal cylindrical surface whose axis coincides with the main axis of rotation of the rollers and lateral rigid arms arranged on both sides of the intermediate section. The free ends of the lateral arms include guides. The pump case is provided with paths on which the guides are slidable. The path directions are predefined in order to constrain the displacement of the free ends of the lateral arms and to deform the intermediate section in such a way that the radius of the internal face is modified keeping the axis thereof coinciding with the main axis, thereby making it possible to use a tube having variable characteristics.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to peristaltic pumps with deformabletubing.

2. Description of the Related Art

In general, peristaltic pumps are composed of a frame to which isfastened a motor whose shaft rotates a cage comprising a plurality ofrollers. The rollers are in contact with a deformable tubing that theycompress until it is sealed. The angular displacement of the point ofsealing causes, behind the compressed zone, a vacuum in the tubing thatimmediately fills with fluid. The amount of fluid trapped in thedeformable tubing between two rollers is then propelled to the outlet ofthe pump. A liquid, pumped at an open end of the deformable tubing,called the intake or upstream end, is thus conveyed to the other end ofthe deformable tubing, called the delivery or downstream end. Mostperistaltic pumps comprise a casing having a cylindrical inner surface,called the bearing surface, against which the tubing is compressed bythe rollers to seal it. The envelope swept by the paths of the outersurfaces of the rollers is called the runway or rolling path.

The main component of a peristaltic pump is its pump body tubing, whichis generally made of elastomer. The pump body tubing is made byextrusion. The physical and dimensional properties of the tubing givenby the manufacturer are only average values. The measured values of aparticular property fluctuate statistically, for example according toGauss' Law, about the corresponding average value. The deformable tubingmanufacturer defines a tolerance interval around the average value inwhich there is an increased probability of finding the measured value ofthe property. The measured thickness of a deformable tubing at the pointwhere it is deformed fluctuates about the average value. It is thereforeprobable that the portion of deformable tubing compressed by the rollershas walls whose combined thickness is less than or greater than thenominal sealing dimension provided for by the pump manufacturer.Incidentally, the sealing of the pump body tubing, characterized by thesealing dimension, consists in first placing the two walls of the tubingin contact and then applying an appropriate clamping action depending onthe thickness of the tubing, its hardness, the temperature, etc.

Similarly, during the use of the deformable tubing, the wall suffersfrom wear, swelling, loss of thickness, modification of the physicalnature of the material of which the tubing is made, etc. This wear inthe broad sense may be due to the repeated mechanical action of therollers on the outer surface of the tubing, to the chemical action ofthe liquids conveyed within the tubing on the inner surface of thetubing, or to the conditions under which the peristaltic pump is used,for example temperature. Consequently, the combined thickness of thewalls of the deformable tubing tends to vary over time. The time comeswhen the cumulative thickness of the walls becomes less than or greaterthan the nominal sealing dimension.

When the nominal sealing dimension is not complied with, either theperistaltic pump becomes less efficient because the seal is notachieved, or the excessive thickness leads to excessive clamping,increasing the resistive torque of the peristaltic pump.

For a given type of tubing, there is therefore a need for a peristalticpump that can compensate for variations in the properties of the tubing.

Moreover, it must be possible for a user to be able to replace a firsttubing by a second pump body tubing rapidly. The adjustments required inorder for the peristaltic pump to be able to operate with a secondtubing must be easy to carry out, and preferably automatic, minimizingrisks of error.

Moreover, in the medical field in particular, the deformable tubing mustbe completely changed for each new application, in particular forreasons of hygiene. There is a permanent need to simplify the consumableso as to increase the number of parts that can be reused from oneapplication to the next, to reduce the operating cost of the pump andthe number of components, often made of plastic, that are thrown away oneach new application.

To solve these various problems, the manufacturers of peristaltic pumpshave to find mechanical solutions that will guarantee sealing. The bestknown solutions consist in mechanically varying the radial distancebetween the inner surface of the bearing surface and the rolling pathsof the rollers on the pump body tubing.

Patent SU 1 262 106 of 7 Oct. 1986 discloses an improved peristalticpump for limiting fluctuations in flow rate during use. The flexibletubing is in this case compressed between a plurality of rollers and aflexible U-shaped strip. The curve of the flexible strip is set bytangential adjustment pins connected to the ends of the flexible stripand radial adjustment pins connected to a central portion of theflexible strip. By turning the adjustment pins to a greater or lesserextent, the user gives the flexible strip an optimum shape.

The deformable tubing is compressed until it is sealed only against thecentral portion of the flexible strip whose profile is an arc of acircle with an opening of 360°/κ and a radius r₁=r₀+2e (where κ is thenumber of rollers and r₀ is the radius of the rolling path run by therollers). The profile of the input and output sections is curved andfollows the equation r₂=r₁+D 2r (where r is the internal radius of thetubing and D a parameter corresponding to the degree of compression ofthe tubing varying between 0 and 1).

That document does not describe how the deformable tubing is insertedbetween the flexible strip and the rollers. Although in the aboveequations the thickness and the radius of the deformable tubing are inthe form of parameters, the use of deformable tubing having variableproperties is not discussed. No particular information about thevariation of the parameter D along the input and output sections isgiven in order to define the optimum profile. Lastly, the curve of theflexible strip is adjusted manually by the user during operation of thepump.

Patent SU 794 243 of 7 Jan. 1981 describes a peristaltic pump whosetubing support is wound to form a helical turn around a roller mountedon a shaft that is off-centre with respect to the axis of the helix. Thedeformable tubing is placed between the roller and the tubing support.The tubing support consists of a metal strip having a degree ofelasticity whose tubing ends are joined by an adjustment screw. When theuser turns the screw, the two ends of the strip move towards or awayfrom one another. As a result, the radius of the helix is modified tochange the distance between the tubing support and the roller to modifythe occlusion of the deformable tubing making it possible to compensatefor the thickness of the tubing.

Moreover, the tubing support is connected to the frame by a series ofbolts that are distributed regularly in an annular arrangement, eachengaged in a guide groove. The guide grooves, whose shape is notdescribed, make it possible indirectly to limit the displacement of thetubing support so that it has a constant radius of curvature all alongits length. Once the user has made the adjustment, the bolts aretightened, which prevents any modification of the radius duringoperation of the pump.

Lastly, U.S. Pat. No. 5,549,461, granted on 27 Aug. 1996, discloses aperistaltic pump comprising an occluder ring linked to a hinged supportby means of a series of threaded bolts. While the rollers are turning,the hinged support is lowered so that the deformable tubing iscompressed against the occluder ring, thus functioning as a clutch forthe pump. In the lowered position, the hinged support is kept againstthe frame by a closure system that prevents excessive pressure ifnecessary. The radius of the occluder ring, which is concentric with theaxis of rotation of the rollers, can be adjusted by the user by means ofa series of screws to allow the pump to be used with deformable tubingof different thicknesses.

The peristaltic pump described is not made for delicate laboratory ormedical applications. The curvature of the ring and the means ofobtaining it by screwing the bolts are not described.

SUMMARY OF THE INVENTION

The aim of the invention is to provide another technical solution to theproblems set out above and to overcome the abovementioned drawbacks.

The subject of the invention is therefore a peristaltic pump, designedto operate with a deformable flexible pump body tubing, comprising ashell, a bearing surface forming a casing with the shell, and aplurality of cylindrical rollers housed inside the casing, the rollersbeing rotatable about a main axis and able to compress the tubing atleast one point on a surface of the bearing surface, facing the insideof the casing, known as the inner surface, characterized in that thebearing surface comprises an intermediate deformable portion with anintermediate inner surface having the shape of a cylinder whose axiscoincides with the main axis, and first and second rigid side arms oneither side of the deformable intermediate portion, first and secondfree ends of the first and second rigid side arms comprising,respectively, first and second guide means, and in that the shellcomprises upstream and downstream tracks on which the first and secondguide means can slide, the upstream and downstream tracks havingrespective predefined paths for limiting the displacement of the firstand second free ends of the first and second rigid side arms so as todeform the deformable intermediate portion so that the radius of theintermediate inner surface is modified while leaving the axis of theintermediate inner surface in coincidence with the main axis, so thatthe peristaltic pump adapts automatically to a tubing having variablephysical and geometric properties.

Preferably, the bearing surface is removable to allow a pump body tubingto be positioned between at least one roller of the plurality of rollersand the intermediate inner surface of the deformable intermediatesection of the bearing surface.

Also preferably, the bearing surface is placed on the shell of theperistaltic pump during the starting up of the peristaltic pump.

Preferably, the bearing surface is placed on the shell by snapping thefirst and second guide means onto the upstream and downstream tracks.

Preferably, the shell consists of the combination of an inner componentand an outer component, the bearing surface being joined to the outercomponent so as to optionally form an interchangeable subassembly with apump body tubing, the interchangeable subassembly being placed on theinner component of the shell during the starting up of the peristalticpump.

Preferably, the peristaltic pump is symmetrical about a main plane ofsymmetry defined by the main axis and the bisector of the angle ofopening of the intermediate inner surface.

Preferably, the variation in the radius of the intermediate innersurface with respect to the radius at rest of the intermediate innersurface is no more than 10%.

Preferably, the plurality of rollers consists of three rollers and theintermediate inner surface has an angle of opening of at least 120° sothat, at any time, at least one of the three rollers is opposite theintermediate inner surface, the tubing being compressed at least onepoint.

Also preferably, the length of the first and second side arms is between0.9 and 1.2 times the value of the radius at rest (R) of theintermediate inner surface.

Preferably, the predefined path of the upstream and downstream tracks iscomparable to first and second line segments lying in a planeperpendicular to the main axis, the segments each making an angle ofabout 45° with the main plane.

In another embodiment, the predefined path of the upstream anddownstream tracks is comparable to arcs of a circle, the centre of whichlies in a plane perpendicular to the main axis.

Preferably the first and second guide means consist of first and secondbosses situated laterally on the respective free ends of each of thefirst and second side arms, and able to slide respectively along theupstream and downstream tracks.

Preferably, the upstream and downstream tracks consist of chamferedlateral surfaces of first and second main walls of the shell.

In another embodiment, the upstream and downstream tracks consist oflateral surfaces of recesses made in the first and second main walls ofthe shell.

In a variant, the upstream and downstream tracks are notched.

Preferably, the bearing surface comprises secondary guide means locatedat the apex of the deformable intermediate portion and projectinglaterally on either side of the latter, and the shell comprises firstand second grooves made, in the main plane of symmetry, in first andsecond main walls of the shell, the grooves being designed to cooperatewith the secondary guide means to keep the bearing surface symmetricalabout the main plane of symmetry during operation of the peristalticpump.

Preferably, the pump comprises storage means which enable the bearingsurface to be held in place on the shell so that the pump body tubing isnot stressed during storage of the pump, the storage means allowing thebearing surface to be correctly positioned during use of the pump.

Preferably, the shell comprises upstream and downstream fixedcounter-bearing surfaces that are placed respectively facing first andsecond inner surfaces of the first and second side arms to keep thetubing stationary with respect to the bearing surface during use of theperistaltic pump.

Preferably, the pump comprises a removable pre-assembled subassemblyconsisting at least of a bearing surface and a tubing.

The invention also relates to a pre-assembled subassembly consisting ofat least a bearing surface and a tubing for a peristaltic pump accordingto one of the pumps described above.

Preferably, the subassembly also comprises an outer shell component, theouter component having tracks.

The invention also relates to a pre-assembled subassembly consisting ofa bearing surface and a tubing for a peristaltic pump as describedabove.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The invention will be more clearly understood, and further aims,details, characteristics and advantages thereof will emerge more clearlyfrom the following description of a particular embodiment of theinvention, which is given solely by way of non-limiting illustration,with reference to the appended drawings. In these drawings:

FIG. 1 is an exploded perspective view of the preferred embodiment ofthe peristaltic pump according to the invention;

FIG. 2 is a side view of the peristaltic pump of FIG. 1, one of thehalf-shells being removed for clarity;

FIG. 3 is a section along the plane III-III, the main plane of symmetryP, of the peristaltic pump of FIG. 2;

FIG. 4 is a diagram of the forces acting on the movable bearing surfaceof the peristaltic pump of FIG. 1;

FIG. 5 is a series of curves showing various profiles of the movablebearing surface of the peristaltic pump of FIG. 1;

FIG. 6 is a perspective view of another embodiment of the peristalticpump according to the invention; and

FIG. 7 is a side view of yet another embodiment of the peristaltic pumpaccording to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The currently preferred embodiment of the peristaltic pump according tothe invention will now be described with reference to the appendedfigures.

With reference to FIGS. 1 to 3, the peristaltic pump 100 comprises ashell 200, a drive device 300, a movable bearing surface 400 and adeformable pump body tubing 500 (shown in chain line in FIG. 2).

The shell 200 is composed of a first half-shell 201 and a secondhalf-shell 202. The first and second half-shells are strictly identical.If they are made of plastic, as in the currently preferred embodiment,each of the two half-shells may be moulded using a single mould.

The first half-shell 201 will now be described in detail. Everythingthat will be said about the first half-shell 201 applies identically tothe second half-shell 202. Consequently, each element of the secondhalf-shell 202 bears the same reference number as the correspondingelement of the first half-shell 201, increased by one unit.

The first half-shell 201 comprises a first main wall 203. When the firstand second half-shells 201 and 202 are assembled together, the surfaceof the first main wall 203 facing the second half-shell 202 is calledthe “first inner surface” 205 a. The surface of the first main wall 203opposite the first inner surface 205 a is called the “first outersurface” 205 b.

The first main wall 203 has the overall shape of an isosceles triangle.In FIG. 2, the base of this triangle is situated “horizontally” and theheight from the base is situated “vertically”. The qualifiers“horizontal” and “vertical” are arbitrary and do not presuppose aparticular orientation of the peristaltic pump but simply give arelative orientation to the elements they describe. The planeperpendicular to the base which contains the height will be called the“main plane of symmetry” and will be denoted P in this document.

On the side of the first inner surface 205 a, the first main wall 203has a bore 207 whose axis A, which is horizontal in FIG. 2, lies in themain plane of symmetry P. The bore 207 has a shoulder 209. The end wallof the bore 207 has a hole 211 passing through the first main wall 203that can accommodate, without friction, a drive shaft 301, as will bedescribed below.

Moreover, the first inner surface 205 a comprises a strengthening wall213 projecting perpendicularly to the said main wall 203. Thestrengthening wall 213 has a height H (FIG. 3). As shown in FIG. 2, thestrengthening wall 213 has a complex shape that is symmetrical about themain plane of symmetry P. The strengthening wall 213 comprises a centralportion 213 a in the shape of an arc of a circle of axis A, a firstupstream release portion 213 e and a first upstream counter-bearingsurface portion 213 f on the intake side (left hand side in FIG. 2), afirst downstream counter-bearing surface portion 213 b and a firstdownstream release portion 213 c on the delivery side (right hand sidein FIG. 2), and lastly a base portion 213 d connects the first upstreamrelease portion 213 e and the first downstream release portion 213 c.

At the junction between the first downstream 213 b or upstream 213 fcounter-bearing surface portions and first downstream 213 c or upstream213 e release portions, the support wall 213 is provided, on thedelivery side, with a female positioning means 215 and, on the intakeside, with a male positioning means 217.

Lastly, the main wall 203 is chamfered. The identical angles of theisosceles triangle which is formed by the main wall 203 (the angles madeat the base of the said wall) are cut off. In this way, the main wall203 has at its periphery a first upstream lateral surface 221 and afirst downstream lateral surface 223. Note that the first upstream anddownstream lateral surfaces 221 and 223 make an overall angle of 135°with the base of the main wall 203.

The second half-shell 202, which is identical to the first half-shell201, is turned around by 180° and faces the first half-shell 201. Thusthe first male positioning means 217 is housed inside the second femalepositioning means 216 and the first female positioning means 215 housesthe second male positioning means 218. Thus the second half-shell 202 iscorrectly positioned laterally with respect to the first half-shell 201.The two half-shells are brought together until the first strengtheningwall 213 comes into contact, over its entire section, with the secondstrengthening wall 214. In this way, the first and second main walls 205and 206 are both parallel and held a predetermined distance from oneanother which is equal to 2H. The two half-shells 201 and 202 are heldin this correct assembly position by adhesive bonding, screws or anyother known means.

When the two half-shells 201 and 202 are assembled, the first bore 207and the second bore 208 form the casing for the peristaltic pump 100.

Moreover, the first and second upstream lateral surfaces 221 and 222form an upstream guide surface or track 251, and the first and seconddownstream side surfaces 223 and 224 form a downstream guide surface ortrack 252.

The drive device 300 comprises a separator 305 with a through hole 306at its centre. The separator 305 has a plurality of rods distributedregularly in an annular arrangement, mounted perpendicularly to theplane of the separator. Each of the rods of the plurality of rods bearsa cylindrical roller that can rotate freely. In the currently preferredembodiment, the separator 305 has three rods 311, 312 and 313 and threerollers 321, 322 and 323. Each roller is therefore spaced angularly fromits neighbour by 120°.

When the first and second half-shells 201 and 202 are assembledtogether, the drive means 300 are housed in the casing formed by thefacing first and second bores 207 and 208. The separator 305 isaccommodated without friction and is therefore free to rotate at the endwall of the first bore 207, beyond the first shoulder 209.

When the two half-shells 201 and 202 are in the assembled position, theheight h of a cylindrical roller is such that a first end of the rolleris positioned inside the first shoulder 209 and the second end of theroller is positioned inside the second shoulder 210 (FIG. 3). If lcorresponds to the depth of the shoulders 209 and 210, the followingrelationship holds: 2H<h<2H+2l.

The frame of the peristaltic pump 100 thus formed is mounted on thedrive shaft 301 of a motor, for example an electric motor (not shown)that can rotate the said rollers 321, 322 and 323.

The drive shaft 301 passes through the first hole 211 and the hole 306in the separator 305. The drive shaft 301 is then force-fitted betweenthe plurality of rollers. The latter are then pressed against the firstand second axial surfaces 209 a and 210 a of the first and secondshoulders 209 and 210. Lastly, the drive shaft 301 passes through thesecond hole 212 in the second wall 204 of the second half-shell 202.

The rotation of the drive shaft is transmitted to the rollers simply bythe rolling, without slipping, of the drive shaft 301 on the outer axialsurfaces of the rollers 321, 322, 323. The rollers run around the firstand second axial surfaces 209 a and 210 a of the first and secondshoulder 209 and 210. The first and second axial surfaces 209 a and 210a therefore define, respectively, first and second rolling paths ofradius r.

The movable bearing surface 400 comprises an intermediate portion 401and first and second side arms 403 and 404, one on either side of theintermediate portion 401. The movable bearing surface 400 is symmetricalabout a plane of symmetry which, when the movable bearing surface isassembled on the frame of the peristaltic pump, corresponds to the mainplane of symmetry P.

The intermediate portion 401 has a shape corresponding to a portion of aring of axis A′ and rectangular cross section. The ring portion extendsangularly on either side of the main plane of symmetry P over an arc ofhalf-angle α at the peak, the peak or apex corresponding to the point B.The intermediate inner surface 405 of the intermediate portion 401 isthe radially inner axial surface of the ring.

In the currently preferred embodiment, the first and second side arms403 and 404 are straight. As a variant, and to solve problems ofergonomy and of space available in some applications, the side arms maybe in other forms: bent, with an angle of rectangular section. Thesurface of the first side arm 403 that is joined tangentially to theintermediate inner surface 405 of the intermediate portion will becalled the first inner surface 407 of the first side arm 403. Likewise,the second side arm 404 has a second inner surface 408 joinedtangentially to the intermediate inner surface 405.

Moreover, the first and second side arms 403 and 404 respectivelycomprise, at their free end, away from the end joined to theintermediate portion 401, grip means, means for holding the tubing, andguide means.

The grip means 409 are formed as one piece with the side arms by bendingthe end portion of the corresponding side arm outwards from the movablebearing surface 400. The first and second side arms 403 and 404respectively have a bend at the point E and F.

The tubing holding means consist of a part 411 (412) in the form of anarch, whose central portion is joined to the inner surface 407 (408), inthe width thereof, at the point E (F). The tapered legs 411 a and 411 b(412 a and 412 b) of the arch project away from the first inner surface407 (408).

In the currently preferred embodiment, the first guide means 413 consistof first edges 413 a and 413 b. The grip means 409 are wider than thefirst side arm 403 so as to form front and rear bearings on either sideof the said arm. These front and rear bearings respectively comprise twobosses which form, where they meet, a first front edge 413 a and a firstrear edge 413 b. Note that the first front edge lies in the extension ofthe first rear edge.

Likewise, the second side arm 404 has second guide means 414, the latterconsisting of second front and rear edges 414 a and 414 b.

The movable bearing surface 400 has a degree of flexibility in theintermediate portion 401. By contrast, the first and second side arms403 and 404 are rigid. In this embodiment, the movable bearing surfaceis made as a single piece by moulding a plastic. It is thereforenecessary for the intermediate portion 401 to be thinner than the firstand second side arms 403 and 404. As the intermediate inner surface 405is joined tangentially to the first and second inner surfaces of theside arms and there is no discontinuity on the inner surface of themovable bearing surface 400, the variation in thickness between theintermediate portion 401 and each of the first and second side arms 403and 404 is made up for on the outer surface of the movable bearingsurface 400 at the end points C and D of the intermediate portion 401.

In the alternative embodiment shown in FIGS. 6 and 7, the movablebearing surface is made of metal. It is obtained by cutting out a metalplate followed by shaping to produce an elastically deformable strip.This variant enable a movable bearing surface to be obtained which hasvery precise physical characteristics, such as the Young's modulus whichcharacterizes its elasticity. In this case, the thickness of the movablebearing surface is reduced.

A pump body tubing 500 is positioned against the inner surface of themovable bearing surface 400. More particularly, the tubing is insertedso as to be slightly pinched, upstream between the legs 411 a and 411 bof the first arch 411 and downstream between the legs 412 a and 412 b ofthe second arch 412. No longitudinal stress is applied to the tubing ifit is correctly positioned along the movable bearing surface. Themovable bearing surface 400, with the tubing 500 placed on it, is thenclipped in position on the peristaltic pump frame. The user moves thefirst and second grip means 409 and 410 apart so as to deform themovable bearing surface 400 at its intermediate portion 401 until theguide means 413 and 414 have cleared the widest section of the frame 200corresponding to the end portions of each of the upstream and downstreamtracks 251 and 252. Once they have cleared it the user lets go of thegrip means. The movable bearing surface 400 then fits itself correctlyon the frame under the effect of forces as will be described later on.

In the correct position of assembly, the axis A′ of the intermediatering-shaped portion 405 coincides with the turning axis A of therollers. In this way, the inner surface of the movable bearing surfacecloses the casing formed within the frame of the peristaltic pump. Themovable bearing surface 400 is also positioned symmetrically on eitherside of the main plane of symmetry P. The correct positioning of themovable bearing surface 400 is automatic. The user does not have to makeany particular adjustments.

In the assembled position, the intermediate portion 405 is housedbetween the first and second main walls 203 and 204 of the twohalf-shells 201 and 202. The width L of the movable bearing surface istherefore slightly less than 2H.

As shown in FIG. 3, the deformable tubing 500 is axially between the tworolling paths 209 a and 210 a and radially between the inner surface ofthe movable bearing surface 400 and at least one of the rollers 321, 322or 323. As a result, in order for the deformable tubing to be compressedby at least one of the rollers at all times, the angle of opening 2α ofthe intermediate portion 401 must be greater than the angle between twosuccessive rollers. In this case, since the drive device 300 has threerollers, the angle of opening 2α must be greater than 120°, this beingthe case whatever the opening of the movable bearing surface. The worstcase being when the bearing surface is very open, i.e. when the guidemeans 413 and 414 are close to the widest section of the shell 200, i.e.in the top part of the tracks 251 and 252.

The compression of the deformable tubing 500 by at least one of therollers is expressed as: R=r+2δe, in which R is the radius of theintermediate inner surface 405 of the intermediate portion 401; r is theradius of the rolling paths 209 a and 210 a, which is a geometricconstant of the peristaltic pump 100; e is the thickness of thedeformable tubing 500; and δ is a parameter dimensionless less thanunity, representing the compression of the two walls of the tubing, oneagainst the other, in order to obtain the nominal sealing dimension.

Moreover, along the first side arm 403, the deformable tubing 500 isslightly compressed between the first inner surface 407 and a facingupstream counter-bearing surface which consists of the first upstreamcounter-bearing surface portion 213 f of the first strengthening wall213 and the second upstream counter-bearing surface portion 214 b of thesecond strengthening wall 214. In an identical manner, along the secondside arm 404, the deformable tubing 500 is slightly compressed betweenthe second inner surface 408 and a facing downstream counter-bearingsurface which consists of the first downstream counter-bearing surfaceportion 213 b of the first strengthening wall 213 and the seconddownstream counter-bearing surface portion 214 f of the secondstrengthening wall 214. In this way, during operation of the peristalticpump 100, the deformable tubing 500 is not entrained by the movement ofthe rollers.

To physically explain how the peristaltic pump 100 with movable bearingsurface 400 works, the particular case of a static positioncharacterized by the fact that the axis of the roller 323 which iscompressing the tubing 500 is in the plane of symmetry P will bedescribed in detail. The way the movable bearing surface 400automatically adapts to various types of tubing and the dynamicoperation of the peristaltic pump will be understood from thischaracteristic position.

With reference to FIG. 4, a tubing 500 of thickness e is compressed bythe roller 323. This roller applies a radial compression force F on thetubing. The compression force F is weak when the tubing 500 is beingdeformed by moving its walls closer together, then it jumps andincreases rapidly once the two walls are brought into contact with oneanother.

For example, if the tubing 500 is already at its sealing dimension butis too close to the axis of rotation A, the roller will apply anexcessive compression force F. We will show below how the movablebearing surface 400 moves so as to move the tubing 500 away from theaxis of rotation A.

The compressed tubing 500 transmits the compression force F to themovable bearing surface 400 at the point of contact, in this case theapex B. Moreover, the movable bearing surface 400 is held at the freeends of the side arms by the first and second edges 413 and 414 incontact with the upstream and downstream tracks 251 and 252.Consequently, the force of the tubing on the movable bearing surface istransmitted by the bearing surface as far as the point of contact of thebearing surface with the shell. A force F₁ corresponding to half theforce F is applied by the first edge to the upstream track 251, and aforce F₂ corresponding to half the force F is applied by the second edgeto the downstream track 252.

The force F₁ is made up of a force F_(1N) that is perpendicular and aforce F_(1T) that is tangential to the upstream track 251.

Assuming that the coefficient of friction, the reaction of the upstreamtrack on the first edge is perpendicular to the upstream track, thereaction of the upstream track only compensates for the force F_(1N).Likewise, the reaction of the downstream track on the second edge onlycompensates for the perpendicular component F_(2N). As a result, thefirst and second free ends of the first and second side arms arerespectively subjected to resultant forces corresponding to thecomponents F_(1T) and F_(2T) of the forces F₁ and F₂.

The components F_(1T) and F_(2T) have a contribution in the plane ofsymmetry P tending to displace the movable bearing surface 400 upwards.The components F_(1T) and F_(2T) also have contributions perpendicularto the plane of symmetry P and in opposite directions, tending toseparate the first and second free ends of the first and second sidearms.

The shape of the movable bearing surface 400 is designed such that thisseparation of the first and second free ends only deforms theintermediate portion 401 of the movable bearing surface 400. Thisdeformation, combined with the upward movement of the movable bearingsurface 400, is reflected in a increase ΔR in the value of the radius Rof the intermediate inner surface 405 without any modification of theposition of the centre of curvature of the intermediate inner surface405, the axis A′ of the intermediate inner surface 405 coincidingpermanently with the axis of rotation A of the rollers. Thus there is anautomatic increase in the radius of the bearing surface against whichthe tubing 500 is compressed. This movement of the bearing surfacecauses the tubing to take up a position a little further away from therollers corresponding to its nominal sealing dimension.

The bearing surface 400 acts as a leaf spring. The more the intermediateportion is deformed, the greater the reaction force applied by thebearing surface on the tubing. This reaction force eventuallycounterbalances the compression force F of the rollers on the tubing. Anequilibrium is gradually created so that the tubing arrives at itsnominal sealing dimension. In this position of equilibrium thetangential components F_(1T) and F_(2T) cancel one another out.

According to this mechanism, sealing of the tubing 500 is ensured nomatter how thick, hard, etc. the tubing is. Sealing is ensured all alongthe angular opening 2α of the intermediate inner surface of theintermediate portion of the movable bearing surface.

Based on this principle of operation, the applicant has carried outcomputer simulations that have enabled it to define a particular profilefor a movable bearing surface for a peristaltic pump for medical use.The components of the pump are made of polyurethane. The pump has aradius r of approximately 18 mm. The radius at rest R of the bearingsurface is 19 mm. The rigid side arms have a length L of 40 mmcorresponding to 2R. The deformations of the profile of the movablebearing surface are shown in FIG. 5. The variation in radius ΔR is equalto about 10% of the value of the radius R, giving a maximum radius of 21mm. As the intermediate portion is deformed, the angle of opening ofthis portion goes from 66° to 60° approximately. The thickness of themovable bearing surface at the intermediate portion is 3 mm, whereas thethickness of the movable bearing surface at the first and second sidearms is 5 mm.

In particular, the computer simulations make it possible to define theshape of the guide tracks 251 and 252 that will allow the free ends ofthe first and second side arms to be held. In FIG. 5, it can be seenthat the upstream and downstream guide tracks are, to a firstapproximation, line segments inclined at 45° to the vertical axis.Advantage is taken of this simple design to make the guide tracks in themain walls of the shell since the range of geometric tolerancesgenerally allowed when making injection-moulded plastic elements, i.e.±0.1 mm, is not exceeded. The above description of the half-shellsinvolved an angle of 135° to the base of the isosceles triangle. In thealternative embodiment shown in FIGS. 6 and 7, more precise tracks aredescribed by arcs of a circle, the centre of which is in the main planeP.

Incidentally, the length of the first and second side arms is ctubingnsuch that the free ends have ample scope for movement making it possibleto vary the radius of the intermediate portion of the movable bearingsurface in small degrees and such that a small amount of force appliedat the free ends of the side arms is converted into a considerablereaction force applied by the bearing surface on the tubing, the sidearms acting as lever arms.

Note that there is a difference in behaviour compared with what has beendescribed above. In FIG. 4, when the roller compressing the tubing isoutside of the plane of symmetry P, the force applied by the tubing tothe movable bearing surface is a radial force M having a componentM_(PT) in the main plane of symmetry P having the effects describedabove, but also a component M_(PP) perpendicular to the said plane ofsymmetry P having the effect of pushing the movable bearing surface 400out of the main plane of symmetry. This is why the apex B of theintermediate portion may have an additional hook included in thethickness of the movable bearing surface 400. This additional metal hookhas an axis parallel to the axis A. The additional hook projects oneither side of the movable bearing surface 400 and engages in first andsecond grooves 251 and 252 (FIG. 7) made respectively in the first andsecond main walls 203 and 204 on the side of the inner surfaces 205 aand 206 a of the said walls. The first and second grooves lie in themain plane of symmetry P. The movable bearing surface 400 is thereforeprevented from moving out of the main plane of symmetry P, theperpendicular component M_(PP) being compensated for by the reaction ofthe additional hook against the side edges of each of the first andsecond grooves 251 and 252.

It also appears that the fact that the movable bearing surface 400 movesslightly out of the main plane of symmetry P has a smoothing effect onthe pressure fluctuations constituting a known conventional phenomenonof peristaltic pumps.

Since the peristaltic pump described above is used for medicalapplications, among others, it is convenient for a pre-assembly composedof a bearing surface and tubing to be offered as a single-use disposableconsumable. The tubing is for example already pinched between the firstand second fastening means and positioned against the inner surface ofthe movable bearing surface. Optionally, the elastomer tubing isadhesively bonded at various points along the inner surface of themovable bearing surface. The pre-assembly thus formed is then packagedin a sterile bag. The characteristics of the tubing and the type offrame onto which the movable bearing surface can be clipped are statedon the bag. The user simply has to unwrap the pre-assembly and clip itonto the corresponding frame.

The immediate advantage is that it allows not only both the electricmotor and the drive shaft 301 to be reused from one application to thenext, as in the prior art, but also the frame assembly consisting of theshell 200 and the drive device 300. The consumable, having a smallernumber of parts, is less expensive. It is easy to position, self-adjustsautomatically and makes it possible to avoid adjustment errors.

Thus the peristaltic pump according to the invention may be used withvarious types of tubing. The variation in the thickness of the walls ofthe tubing, which has various causes (manufacture, wear, different typesof tubing, etc.), is compensated for automatically by the adjustment ofthe radius of the intermediate inner surface of the movable bearingsurface.

FIG. 6 shows another embodiment of the invention. In this embodiment,the shell consists of two components: an inner component (not shown)forming a casing for housing the rollers, and an outer component 260bearing the guide tracks. Once assembled, the inner and outer 260components form a shell similar to the shell 200 described in thecurrently preferred embodiment illustrated in FIGS. 1 to 5.

Two subassemblies can thus be distinguished: first, a fixed subassemblyoptionally comprising the motor, the separator 305, the rollers 321, 322and 323 and the inner component of the shell; and, second, aninterchangeable subassembly comprising a tubing 500, a movable bearingsurface 400 and the outer component 260 of the shell (and hence theguide tracks). The interchangeable subassembly may for example beconnected to a bottle containing liquid to be pumped. The user combinesthe fixed and interchangeable subassemblies to form a peristaltic pumpwith its volume of liquid to be pumped.

Moreover, in FIG. 6, the movable bearing surface 400 consists of a metalstrip comprising an intermediate portion in the shape of an arc of acircle and straight and rigid upstream and downstream side arms oneither side of the intermediate portion. The bearing surface 400 has asmall thickness. In particular, the guide means are upstream 473 a and473 b and downstream 474 a and 474 b bosses consisting of tongues cutout of the mass of the metal strip when it is being cut. The tongues arethen bent back on themselves to form a boss which can slide along theguide tracks.

According to a variant embodiment of the peristaltic pump, the upstreamand downstream guide tracks 251 and 252 are not located on the upstream221 and 222 and downstream 223 and 224 lateral surfaces of the shell,but on the lateral surfaces of recesses made in the main walls of theshell. More particularly, the first main wall 263 of the outer component260 comprises a first upstream recess 265 and a first downstream recess266. Likewise, the second main wall 264 of the outer component 260comprises a second upstream recess 266 and a second downstream recess268. The lateral surfaces 275 and 276 closest to the axis of rotation Aof the recesses 265 and 266, respectively, have a predefined path forforming the upstream track 251. Likewise, the lateral surfaces 277 and278 closest to the axis of rotation A of the recesses 267 and 268,respectively, have a predefined path for forming the downstream track252. Thus, and advantageously for the embodiment of FIG. 7 in which theshell is the combination of two subassemblies, the movable bearingsurface 400 is associated with the outer part 260 of the shell in such away as to join together the constituent components of theinterchangeable subassembly. The movable bearing surface is housed inthe outer part 260, i.e. the bosses 473 a, b and 474 a, b are housed inthe corresponding recesses 265-278 when the main walls 264 and 263 ofthe outer part 260 are superposed.

Note that the guide tracks are in the form of arcs of a circle, thecentre of which is in the main plane P. This particular path of thetracks results from the particular geometric characteristics of thisembodiment of the peristaltic pump (length of the lever arms of the sidearms, range of tubes usable in this pump, etc.), the greater precisionachieved in production of the tracks by moulding, and the use of a metalmovable bearing surface manufactured with great precision.

FIG. 7 shows yet another embodiment of the invention. In thisembodiment, the first and second upstream and downstream lateralsurfaces are no longer smooth surfaces, but comprise a plurality ofmillimetric notches 280. The shape of each notch 280 is asymmetrical. Anotch consists of a short surface 281, oriented in the direction of themain plane of symmetry P, making a large angle with the tangent of thepath of the track 251 or 252, and a long surface 282, oriented away fromthe main plane of symmetry P, making a small angle with the tangent tothe path of the track 251 or 252.

Thus, the bosses 473 a, b and 474 a, b of the movable bearing surface400 can move along the track 251 and the track 252 only in the directionof clamping of the tubing 500, i.e. towards the main plane of symmetryP. This direction is preferred since it corresponds to the normalevolution of a tubing during use, under the effect of wear and the lossof elasticity of the tubing wall. Moreover, this arrangement allows theperistaltic pump to withstand high operating pressures withoutmodification of the radius of curvature, the bosses bearing on the shortsurfaces 281 of the notches 280.

In FIG. 7, the groove 251 for guiding the hook located at the apex ofthe movable bearing surface 400 is shown. It comprises a wedge 290. Thewedge 290 makes it possible, when the peristaltic pump is in the storageposition, to keep the movable bearing surface 400 away from the rollers321-323 so that the pump body tubing 500 is not compressed or stressedduring this period of storage.

To this end, the wedge 290 is of generally parallelepiped shape and canbe inserted in the groove 251. The surface 291 of the wedge 290 whichbears on the roller 323 located in the main plane P is circular. It hasa radius of curvature equal to that of the outer surface of the roller323. The hook located at the apex of the movable bearing surface bearson a surface 292 of the wedge 290 opposite the cylindrical surface 291.

When the user wishes to use the peristaltic pump, the drive motorstrains so as to apply an additional torque so that the roller 323 isreleased from the wedge 290 and can roll along the rolling path 209. Thewedge 290 is then pushed upwards and lifts the movable bearing surface400. Next, once the roller 323 has been released from the wedge 290, thelatter falls down behind the roller 323 into the gap between twosuccessive rollers. The movable bearing surface 400, which is then nolonger supported by the wedge 290, slides along the groove 251 andplaces itself automatically in its correct operating position.

Although the invention has been described in relation to a particularembodiment, it is of course not at all limited to this embodiment andcomprises all technical equivalents of the means described and allcombinations thereof so long as these fall within the scope of theinvention.

1. A peristaltic pump (100), designed to operate with a deformableflexible pump body tubing (500), comprising: a shell (200); a bearingsurface (400) forming a casing with said shell; and a plurality ofcylindrical rollers (321, 322, 323) housed inside said casing, saidrollers being rotatable about a main axis (A) and able to compress saidtubing at least one point on a surface of said bearing surface facingthe inside of said casing, called an inner surface, wherein said bearingsurface (400) comprises an intermediate deformable portion (401) with anintermediate inner surface (405) having the shape of a cylinder whoseaxis (A′) coincides with said main axis, and first and second rigid sidearms (403, 404) on either side of said deformable intermediate portion,first and second free ends (E, F) of said first and second rigid sidearms comprising, respectively, first and second guide means (413, 414),and in that said shell comprises upstream and downstream tracks (251,252) on which said first and second guide means can slide in anassembled position of said pump, said upstream and downstream trackscomprising chamfered lateral surfaces of first and second main walls ofsaid shell and respective predefined paths for limiting the displacementof said first and second free ends of the first and second rigid sidearms so as to deform said deformable intermediate portion so that aradius of said intermediate inner surface is modified while leaving saidaxis of said intermediate inner surface in coincidence with said mainaxis, so that said peristaltic pump adapts automatically to a tubinghaving variable physical and geometric properties.
 2. The peristalticpump according to claim 1, wherein said bearing surface (400) isremovable to allow a pump body tubing (500) to be positioned between atleast one roller of said plurality of rollers (321, 322, 323) and saidintermediate inner surface (405) of said deformable intermediate section(401) of the bearing surface.
 3. The peristaltic pump according to claim2, wherein said bearing surface (400) is placed on said shell (200) ofsaid peristaltic pump (100) during starting up of said peristaltic pump.4. The peristaltic pump according to claim 3, wherein said bearingsurface is placed on said shell by snapping the first and second guidemeans (413, 414) onto said upstream and downstream tracks.
 5. Theperistaltic pump according to claim 2, wherein said shell comprises acombination of an inner component and an outer component (260), saidbearing surface being joined to said outer component so as to optionallyform an interchangeable subassembly with a pump body tubing, theinterchangeable subassembly being placed on said inner component of theshell during starting up of said peristaltic pump.
 6. The peristalticpump according to claim 1, wherein said peristaltic pump (100) issymmetrical about a main plane of symmetry (P) defined by said main axis(A) and a bisector of an angle of opening of said intermediate innersurface (405).
 7. The peristaltic pump according to claim 1, wherein avariation in the radius (ΔR) of said intermediate inner surface (405)with respect to a radius at rest (R) of the radius of said intermediateinner surface is no more than 10%.
 8. The peristaltic pump according toclaim 1, characterized in that said plurality of rollers (321, 322, 323)comprises three rollers and said intermediate inner surface (405) has anangle of opening of at least 1200 so that, at any time, at least one ofsaid three rollers is opposite said intermediate inner surface, saidtubing (500) being compressed at at least one point.
 9. The peristalticpump according to claim 1, wherein a length of said first and secondside arms (403, 404) is between 0.9 and 1.2 times the value of a radiusat rest (R) of said intermediate inner surface (405).
 10. Theperistaltic pump according to claim 1, wherein said predefined path ofsaid upstream and downstream tracks is comparable to first and secondline segments lying in a plane perpendicular to said main axis (A), saidsegments each making an angle of about 45° with a main plane.
 11. Theperistaltic pump according to claim 1, wherein said predefined path ofsaid upstream and downstream tracks is comparable to arcs of a circle,the centre of which lies in a plane perpendicular to said main axis (A).12. The peristaltic pump according to claim 1, wherein said first andsecond guide means comprise first and second bosses (413, 414) situatedlaterally on the respective free ends of each of said first and secondside arms (403, 404), and able to slide respectively along said upstreamand downstream tracks.
 13. A peristaltic pump (100), designed to operatewith a deformable flexible pump body tubing (500), comprising: a shell(200); a bearing surface (400) forming a casing with said shell; and aplurality of cylindrical rollers (321, 322, 323) housed inside saidcasing, said rollers being rotatable about a main axis (A) and able tocompress said tubing at least one point on a surface of said bearingsurface facing the inside of said casing, called an inner surface,wherein said bearing surface (400) comprises an intermediate deformableportion (401) with an intermediate inner surface (405) having the shapeof a cylinder whose axis (A′) coincides with said main axis, and firstand second rigid side arms (403, 404) on either side of said deformableintermediate portion, first and second free ends (E, F) of said firstand second rigid side arms comprising, respectively, first and secondguide means (413, 414), and in that said shell comprises upstream anddownstream tracks (251, 252) on which said first and second guide meanscan slide in an assembled position of said pump, said upstream anddownstream tracks having respective predefined paths for limiting thedisplacement of said first and second free ends of the first and secondrigid side arms so as to deform said deformable intermediate portion sothat a radius of said intermediate inner surface is modified whileleaving said axis of said intermediate inner surface in coincidence withsaid main axis, so that said peristaltic pump adapts automatically to atubing having variable physical and geometric properties, and whereinsaid upstream and downstream tracks consist of lateral surfaces ofrecesses made in the first and second main walls of said shell.
 14. Theperistaltic pump according to claim 1, wherein the upstream anddownstream tracks are notched.
 15. The peristaltic pump according toclaim 1, wherein said bearing surface (400) comprises secondary guidemeans mechanisms located at the apex (B) of said deformable intermediateportion (405) and projecting laterally on either side of the latter, andin that said shell (200) comprises first and second grooves (251, 252)made, in said main plane of symmetry (P), in first and second main walls(203, 204) of said shell, said grooves being designed to cooperate withsaid secondary guide mechanisms to keep the bearing surface symmetricalabout said main plane of symmetry during operation of said peristalticpump.
 16. The peristaltic pump according to claim 1, wherein theperistaltic pump further comprises storage means which enable saidbearing surface to be held in place on said shell so that said pump bodytubing is not stressed during storage of said pump, said storage meansallowing the bearing surface to be correctly positioned during use ofsaid pump.
 17. The peristaltic pump according to claim 1, wherein saidshell (200) comprises upstream and downstream fixed counter-bearingsurfaces that are placed respectively facing first and second innersurfaces (407, 408) of said first and second side arms (403, 404) tokeep the tubing (500) stationary with respect to said bearing surface(400) during use of said peristaltic pump.
 18. The peristaltic pumpaccording to claim 1, wherein the peristaltic pump further comprises aremovable pre-assembled subassembly consisting at least of a bearingsurface (400) and a tubing (500).